132 FLOWERS OF ROCKS, WALLS, ETC. 



attached to humus, such as collects in the vertical or horizontal clefts 

 in exposed rocks. The clefts caused naturally by alternate heat and 

 cold, frost, disintegration, rain or chemictd action are not inconsiderable, 

 and support a typical plant formation, which varies accordinij to the 

 exposure, size of cleft, position, &c. Chasmophytic veoetation may be 

 found in other situations, as where Orpine grows under hedge-banks, 

 though its true position is in the clefts of rocks. 



Chasmophytes develop rhizoids, and have flattened rootlets and 

 tap-roots. They are usually tufted, and many are rosette plants. 



They are xerophylous as a whole, such as Sedum or Stone Crop, 

 Saxifrages, Sempervivum, and Draba. Many species of Chickweed, 

 Sandwort, Speedwell, Lady's Mantle, Saxifrage are w^hite and woolly. 

 Most of them are perennials, and while most are Xeroplntes, some are 

 Mesophytes, and along the shore Halophytes. 



If we take the flowers that orrow on older rocks we have here 

 an example in Sandwort Spurrey, which is found on granitic and 

 slaty or schistose rocks, where also, if there is some detritus, another 

 Chomophyte, Bird's-foot, grows. The Field Mouse-ear and Silvery 

 Hair Grass grow on similar sand-rock soil, and may also be found on 

 marlstone on little detritus; and in the hollows of the slopes from the 

 escarpment of the latter one finds the White Meadow Saxifrage, which 

 prefers clay soil derived from the Middle Lias clays. Limestone rocks 

 with little soil are the only habitat on which Cheddar Pink grows. 

 The chalk, which forms but a thin rubble, or has otherwise a sandy, 

 gravelly subsoil, affords support for Horseshoe Vetch, with its pretty 

 horseshoe-like pods, and Yellow Centaury is found there or on lime- 

 stone, but usually in wetter stations. 



The Chasmophytes include such rupeslrals as Navelwort, Orpine, 

 Golden-rod, the last growing in tufts, tall and graceful, with rich golden 

 blooms. Golden-rod is either a Chasmophyte or a Mesoph)te, growing 

 in chalky districts along the roadside in hedge bottoms. 



Mouse-ear Hawkweed sometimes covers exposed rocks growing 

 in the crannies on the faces of e.xposures, and extends above vertically 

 on a sand-rock soil or a lime-rock soil, or it may also be found on wall- 

 tops. Out of the crevices in the Marlstone Rock-bed, or on older 

 detrital rocks such as slate, one may see Wall Lettuce growing in the 

 shade sheltered by overhanging herbage. 



Walls have a typical flora, but this mural habitat is an entirely 

 artificial one, originated within the historic era. Here, in towns and 

 villages throughout the country from Land's End to John o' Groats, 

 one may find the Yellow I'^imitory in gardens or on greenhouse walls 



